Helping decisions and kin recognition in long-tailed tits: is call similarity used to direct help towards kin?

Abstract

Most cooperative breeders live in discrete family groups, but in a minority, breeding populations comprise extended social networks of conspecifics that vary in relatedness. Selection for effective kin recognition may be expected for more related individuals in such kin neighbourhoods to maximize indirect fitness. Using a long-term social pedigree, molecular genetics, field observations and acoustic analyses, we examine how vocal similarity affects helping decisions in the long-tailed tit Aegithalos caudatus . Long-tailed tits are cooperative breeders in which help is typically redirected by males that have failed in their own breeding attempts towards the offspring of male relatives living within kin neighbourhoods. We identify a positive correlation between call similarity and kinship, suggesting that vocal cues offer a plausible mechanism for kin discrimination. Furthermore, we show that failed breeders choose to help males with calls more similar to their own. However, although helpers fine-tune their provisioning rates according to how closely related they are to recipients, their effort was not correlated with their vocal similarity to helped breeders. We conclude that although vocalizations are an important part of the recognition system of long-tailed tits, discrimination is likely to be based on prior association and may involve a combination of vocal and non-vocal cues. This article is part of the theme issue ‘Signal detection theory in recognition systems: from evolving models to experimental tests’.

Kith or Kin? Familiarity as a Cue to Kinship in Social Birds

“…Indeed, this suggests a mechanism of phenotype matching, with a gradation of similarity in vocalizations providing a fine-grained, continuous estimation of kinship. However, bioacoustic analysis did not support this suggestion (Leedale et al, 2020), so even in this relatively well-studied system, the mechanism underlying graded discrimination remains unknown.…”

“…Long-tailed tits have a kinselected cooperative breeding system in which failed breeders preferentially redirect their care to help relatives (Russell and Hatchwell, 2001;Hatchwell et al, 2014). Playback experiments show that long-tailed tits are able to discriminate between the calls of close kin and non-kin (Hatchwell et al, 2001;, and the calls thought to be used as recognition cues are individually distinctive, repeatable and more similar among close kin than among non-kin Leedale et al, 2020). Cross-fostering experiments showed that nestlings and/or fledglings acquire their recognition templates from familiar kin during an associative learning period, when the cues themselves develop , and that cross-fostered offspring subsequently help at the nest of foster siblings (Hatchwell et al, 2001).…”

“…Cross-fostering experiments showed that nestlings and/or fledglings acquire their recognition templates from familiar kin during an associative learning period, when the cues themselves develop , and that cross-fostered offspring subsequently help at the nest of foster siblings (Hatchwell et al, 2001). Moreover, there is strong evidence for effective discrimination of first-order kin, but not second-order kin, both in the context of helping behavior and mate choice (Leedale, 2018;Leedale et al, 2020). These results are all consistent with the idea that long-tailed tits categorize conspecifics as either kin or non-kin based on early association in the context of brood care .…”

“…These results are all consistent with the idea that long-tailed tits categorize conspecifics as either kin or non-kin based on early association in the context of brood care . On the other hand, Nam et al (2010) and Leedale et al (2020) both found that long-tailed tit helpers modified their effort according to their relatedness to the helped brood, suggesting that assessment of kinship is not based on a simple dichotomous rule of familiar (kin) vs. unfamiliar (non-kin) birds. Indeed, this suggests a mechanism of phenotype matching, with a gradation of similarity in vocalizations providing a fine-grained, continuous estimation of kinship.…”

“…Binary or threshold kin discrimination will be effective in most cooperative breeders living on stable territories that, at least with regard to the helping sex, are mostly made up of first-order relatives, facilitating a decision rule based on prior association (Curry, 1988;Payne et al, 1988;Komdeur et al, 2004). In contrast, a recognition cue that permits individuals to discriminate kin varying in relatedness has been identified only in the bell miner (Wright et al, 2010), even though such fine-scale discrimination has been reported in at least one other species (Nam et al, 2010;Leedale et al, 2020).…”